The present invention relates to a sliding closure unit or slide gate or slide gate nozzle, particularly for use in controlling the discharge of molten metal from a spout of a converter vessel. The present invention particularly is related to such a slide gate nozzle that includes a stationary refractory bottom plate to be positioned stationarily with a discharge opening thereof aligned with an opening of the spout of the converter vessel and a movable refractory slide valve plate mounted for sliding movement relative to the bottom plate such that a discharge opening of the slide valve plate may be brought into and out of alignment with the discharge opening of the bottom plate. The slide valve plate seals against the bottom plate and enables controlled discharge of the molten metal from the spout of the converter vessel. The present invention also relates to a refractory plate assembly employable in such a slide gate nozzle.
A slide gate nozzle of the above described type is disclosed in Swiss CH-PS 647,702. Such known slide gate nozzle includes a refractory bottom plate adjoining directly a runner mortared into the spout of the converter vessel and a refractory slide valve plate which sealingly slides on the bottom plate, and a refractory discharge sleeve mounted on and movable with the slide valve plate. Otherwise, the construction of such known slide gate nozzle corresponds substantially to universally known two-plate slide gates or sliding closure units.
During operation of a converter vessel employing such known slide gate nozzle, the following problems inherently occur. Thus, the diameter of a converter vessel taphole ranges normally from 100 to 200 mm. Therefore, when the slide gate nozzle is installed, the slide gate nozzle itself and also the slide valve plate to be installed therein must be dimensioned correspondingly large. Manipulating such members, for example to change worn plates, can be done only with great difficulty. Particularly, due to the solid and large size construction of the members of the slide gate nozzle, exchange of worn plates normally can be carried out only with the aid of large cranes. A tapping runner of the spout of the converter vessel usually comprises several refractory sleeves, i.e. so-called tapping bricks, that have a service life equal to the time required to achieve from 70 to 130 charges or tappings of the converter vessel. This service life is average according to the current state of the art wherein it is possible to achieve up to 35 charges or tappings per day. Thus, the converter vessel is maintained in service virtually without interruption until it is necessary to replace worn or consumed tapping bricks. However, according to the current state of the art, the service life of the refractory bottom plate and the refractory slide valve plate of the slide gate nozzle is equal only to a maximum of 30 charges or tappings. Therefore, the bottom plate and the slide valve plate have to be replaced a number of times during one intended continuous operation of the converter vessel of up to 130 charges. This means that in fact the operation of the converter vessel is not continuous and uninterrupted, but rather must be interrupted multiple times to replace worn bottom and slide valve plates. This results in unavoidable delays in the use of the converter vessel. Moreover, suitably trained personnel to service the slide gate nozzle must be provided for such replacement operations. Therefore, every day practice has shown that use of such known slide gate nozzle on converter vessels correspondingly is quite cost intensive and even can interfere with the required operational sequence of the converter vessel. Therefore, it in fact has not been practically possible to employ such known slide gate nozzle for controlling the discharge of molten metal from a spout of a converter vessel.